When good grounds turn bad—isolate!

Industrial communication via fieldbus-transceiver systems often requires long transmission lines. Designers, unaware of the large ground-potential differences (GPDs) between remote bus locations, either rely on the local earth ground as a reliable signal return path or directly connect remote grounds to each other—thus creating noisy ground loops. In both cases the integrity of the transmission signal is compromised, which can lead to system lockup and destroy the bus transceivers. This article explains where GPDs originate in the electrical installation, how ground loops are created unintentionally, and how isolation circumvents both conditions to yield a robust data-transmission system.